Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 30 of 94

Full-Text Articles in Physics

Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal Aug 2019

Tunneling Anisotropic Magnetoresistance In Ferroelectric Tunnel Junctions, Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Using a simple quantum-mechanical model, we explore a tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, where spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, whose electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR being dependent on the ferroelectric polarization direction. The SOC change with polarization switching affects tunneling conductance, revealing an alternative mechanism of tunneling electroresistance. These results demonstrate alternative ...


Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov Aug 2019

Magnetoelectric Effect At The Ni/Hfo2 Interface Induced By Ferroelectric Polarization, Qiong Yang, Lingling Tao, Zhen Jiang, Yichun Zhou, Evgeny Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Driven by the technological importance of the recently discovered ferroelectric HfO2, we explore a magnetoelectric effect at the HfO2-based ferroelectric-ferromagnetic interface. Using density-functionaltheory calculations of the Ni/HfO2/Ni (001) heterostructure as a model system, we predict a stable and sizable ferroelectric polarization in a few-nm-thick HfO2 layer. For the Ni/HfO2 interface with opposite polarization directions (pointing to or away from the interface), we find a sizable difference in the interfacial Ni—O bonding, resulting in dissimilar degrees of depletion of the electron density around the interface. The latter affects the relative population ...


A Room-Temperature Ferroelectric Semimetal, Pankaj Sharma, Fei-Xiang Xiang, Ding-Fu Shao, Dawei Zhang, Evgeny Y. Tsymbal, Alex R. Hamilton, Jan Seidel Jul 2019

A Room-Temperature Ferroelectric Semimetal, Pankaj Sharma, Fei-Xiang Xiang, Ding-Fu Shao, Dawei Zhang, Evgeny Y. Tsymbal, Alex R. Hamilton, Jan Seidel

Evgeny Tsymbal Publications

Coexistence of reversible polar distortions and metallicity leading to a ferroelectric metal, first suggested by Anderson and Blount in 1965, has so far remained elusive. Electrically switchable intrinsic electric polarization, together with the direct observation of ferroelectric domains, has not yet been realized in a bulk crystalline metal, although incomplete screening by mobile conduction charges should, in principle, be possible. Here, we provide evidence that native metallicity and ferroelectricity coexist in bulk crystalline van der Waals WTe2 by means of electrical transport, nanoscale piezoresponse measurements, and first-principles calculations. We show that, despite being a Weyl semimetal, WTe2 has switchable spontaneous ...


Anomalous Hall Conductivity Of Noncollinear Magnetic Antiperovskites, Gautam Gurung, Ding-Fu Shao, Tula R. Paudel, Evgeny Y. Tsymbal Apr 2019

Anomalous Hall Conductivity Of Noncollinear Magnetic Antiperovskites, Gautam Gurung, Ding-Fu Shao, Tula R. Paudel, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The anomalous Hall effect (AHE) is a well-known fundamental property of ferromagnetic metals, commonly associated with the presence of a net magnetization. Recently, an AHE has been discovered in noncollinear antiferromagnetic (AFM) metals. Driven by nonvanishing Berry curvature of AFM materials with certain magnetic space-group symmetry, anomalous Hall conductivity (AHC) is very sensitive to the specific type of magnetic ordering. Here, we investigate the appearance of AHC in antiperovskite materials family ANMn3 (A = Ga, Sn, Ni), where different types of noncollinear magnetic ordering can emerge. Using symmetry analyses and first-principles density-functional theory calculations, we show that with almost identical ...


Dirac Nodal Line Metal For Topological Antiferromagnetic Spintronics, Ding-Fu Shao, Gautam Gurung, Shu-Hui Zhang, Evgeny Y. Tsymbal Feb 2019

Dirac Nodal Line Metal For Topological Antiferromagnetic Spintronics, Ding-Fu Shao, Gautam Gurung, Shu-Hui Zhang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Topological antiferromagnetic (AFM) spintronics is an emerging field of research, which exploits the N´eel vector to control the topological electronic states and the associated spin-dependent transport properties. A recently discovered N´eel spin-orbit torque has been proposed to electrically manipulate Dirac band crossings in antiferromagnets; however, a reliable AFM material to realize these properties in practice is missing. In this Letter, we predict that room-temperature AFM metal MnPd2 allows the electrical control of the Dirac nodal line by the N´eel spin-orbit torque. Based on first-principles density functional theory calculations, we show that reorientation of the N´eel ...


Electrically Reversible Magnetization At The Antiperovskite/Perovskite Interface, Ding-Fu Shao, Gautam Gurung, Tula R. Paudel, Evgeny Y. Tsymbal Feb 2019

Electrically Reversible Magnetization At The Antiperovskite/Perovskite Interface, Ding-Fu Shao, Gautam Gurung, Tula R. Paudel, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Using density-functional calculations, we predict the emergence of electrically reversible magnetization at the interface between antiferromagnetic noncollinear antiperovskite GaNMn3 and ferroelectric perovskite BaTiO3. We find that Mn magnetic moments are enhanced and reoriented at the GaNMn3/ATiO3 (001) (A = Sr and Ba) interface, resulting in a sizable net magnetization along the [110] direction. This magnetization is reversed with ferroelectric polarization of BaTiO3 through ∼20◦ rotation of the noncollinear magnetic moments. The effect is driven by ferroelectric modulation of the antiferromagnetic exchange coupling between the interfacial Mn atoms mediated by the Mn-3d orbital population. Our results open opportunities for controlling the ...


Ferroelectric Polarization Control Of Magnetic Anisotropy In Pbzr0.2ti0.8o3/La0.8sr0.2mno3 Heterostructures, Anil Rajapitamahuni, L. L. Tao, Y. Hao, Jingfeng Song, Xiaoshan Xu, Evgeny Y. Tsymbal, Xia Hong Feb 2019

Ferroelectric Polarization Control Of Magnetic Anisotropy In Pbzr0.2ti0.8o3/La0.8sr0.2mno3 Heterostructures, Anil Rajapitamahuni, L. L. Tao, Y. Hao, Jingfeng Song, Xiaoshan Xu, Evgeny Y. Tsymbal, Xia Hong

Evgeny Tsymbal Publications

The interfacial coupling between the switchable polarization and neighboring magnetic order makes ferroelectric/ferromagnetic composite structures a versatile platform to realize voltage control of magnetic anisotropy. We report the nonvolatile ferroelectric field effect modulation of the magnetocrystalline anisotropy (MCA) in epitaxial PbZr0.2Ti0.8O3 (PZT)/La0.8Sr0.2MnO3 (LSMO) heterostructures grown on (001) SrTiO3 substrates. Planar Hall effect measurements show that the in-plane magnetic anisotropy energy in LSMO is enhanced by about 22% in the hole accumulation state compared to the depletion state, in quantitative agreement with our first-principles ...


Enhanced Flexoelectricity At Reduced Dimensions Revealed By Mechanically Tunable Quantum Tunnelling, Saikat Das, Bo Wang, Tula R. Paudel, Sung Min Park, Evgeny Y. Tsymbal, Long-Qing Chen, Daesu Lee, Tae Won Noh Feb 2019

Enhanced Flexoelectricity At Reduced Dimensions Revealed By Mechanically Tunable Quantum Tunnelling, Saikat Das, Bo Wang, Tula R. Paudel, Sung Min Park, Evgeny Y. Tsymbal, Long-Qing Chen, Daesu Lee, Tae Won Noh

Evgeny Tsymbal Publications

Flexoelectricity is a universal electromechanical coupling effect whereby all dielectric materials polarise in response to strain gradients. In particular, nanoscale flexoelectricity promises exotic phenomena and functions, but reliable characterisation methods are required to unlock its potential. Here, we report anomalous mechanical control of quantum tunnelling that allows for characterising nanoscale flexoelectricity. By applying strain gradients with an atomic force microscope tip, we systematically polarise an ultrathin film of otherwise nonpolar SrTiO3, and simultaneously measure tunnel current across it. The measured tunnel current exhibits critical behaviour as a function of strain gradients, which manifests large modification of tunnel barrier profiles ...


Tunable Two-Dimensional Dirac Nodal Nets, Ding-Fu Shao, Shu-Hui Zhang, Xiaoqian Dang, Evgeny Y. Tsymbal Oct 2018

Tunable Two-Dimensional Dirac Nodal Nets, Ding-Fu Shao, Shu-Hui Zhang, Xiaoqian Dang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Nodal-line semimetals are characterized by symmetry-protected band crossing lines and are expected to exhibit nontrivial electronic properties. Connections of the multiple nodal lines, resulting in nodal nets, chains, or links, are envisioned to produce even more exotic quantum states. In this work, we propose a feasible approach to realize tunable nodal-line connections in real materials. We show that certain space group symmetries support the coexistence of the planar symmetry-enforced and accidental nodal lines, which are robust to spin-orbit coupling and can be tailored into intricate patterns by chemical substitution, pressure, or strain. Based on first-principles calculations, we identify nonsymmorphic centrosymmetric ...


Two-Dimensional Type-Ii Dirac Fermions In A Laalo3/Lanio3/Laalo3 Quantum Well, L. L. Tao, Evgeny Y. Tsymbal Sep 2018

Two-Dimensional Type-Ii Dirac Fermions In A Laalo3/Lanio3/Laalo3 Quantum Well, L. L. Tao, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The type-II Dirac fermions that are characterized by a tilted Dirac cone and anisotropic magnetotransport properties have been recently proposed theoretically and confirmed experimentally. Here, we predict the emergence of two-dimensional (2D) type-II Dirac fermions in LaAlO3/LaNiO3/LaAlO3 quantum-well structures. Using first-principles calculations and model analyses, we show that the Dirac points are formed at the crossing between the dx2−y2 and dz2 bands protected by the mirror symmetry. The energy position of the Dirac points can be tuned to appear at the Fermi energy by changing the quantum-well width. For ...


Direct Observation Of Room-Temperature Out-Of-Plane Ferroelectricity And Tunneling Electroresistance At The Two-Dimensional Limit, H. Wang, Z R. Liu, H. Y. Yoong, Tula R. Paudel, J. X. Xia, R. Guo, W. N. Lin, P. Yang, J. Wang, G. M. Chow, T. Venkatesan, Evgeny Y. Tsymbal, H. Tian, J. S. Chen Aug 2018

Direct Observation Of Room-Temperature Out-Of-Plane Ferroelectricity And Tunneling Electroresistance At The Two-Dimensional Limit, H. Wang, Z R. Liu, H. Y. Yoong, Tula R. Paudel, J. X. Xia, R. Guo, W. N. Lin, P. Yang, J. Wang, G. M. Chow, T. Venkatesan, Evgeny Y. Tsymbal, H. Tian, J. S. Chen

Evgeny Tsymbal Publications

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unitcell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films ...


Defect-Assisted Tunneling Electroresistance In Ferroelectric Tunnel Junctions, Konstantin Klyukin, L. L. Tao, Evgeny Y. Tsymbal, Vitaly Alexandrov Aug 2018

Defect-Assisted Tunneling Electroresistance In Ferroelectric Tunnel Junctions, Konstantin Klyukin, L. L. Tao, Evgeny Y. Tsymbal, Vitaly Alexandrov

Evgeny Tsymbal Publications

Recent experimental results have demonstrated ferroelectricity in thin films of SrTiO3 induced by antisite TiSr defects. This opens a possibility to use SrTiO3 as a barrier layer in ferroelectric tunnel junctions (FTJs)—emerging electronic devices promising for applications in nanoelectronics. Here using density functional theory combined with quantum-transport calculations applied to a prototypical Pt/SrTiO3/Pt FTJ, we demonstrate that the localized in-gap energy states produced by the antisite TiSr defects are responsible for the enhanced electron tunneling conductance which can be controlled by ferroelectric polarization. Our tight-binding modeling, which takes into account multiple defects ...


Effects Of B And C Doping On Tunneling Magnetoresistance In Cofe/Mgo Magnetic Tunnel Junctions, Andy Paul Chen, John D. Burton, Evgeny Y. Tsymbal, Yuan Ping Feng, Jingsheng Chen Jul 2018

Effects Of B And C Doping On Tunneling Magnetoresistance In Cofe/Mgo Magnetic Tunnel Junctions, Andy Paul Chen, John D. Burton, Evgeny Y. Tsymbal, Yuan Ping Feng, Jingsheng Chen

Evgeny Tsymbal Publications

Using density-functional theory calculations, we investigate the dominant defects formed by boron (B) and carbon (C) impurities in a CoFe/MgO/CoFe magnetic tunnel junction (MTJ) and their influence on conductivity and tunneling magnetoresistance (TMR). We find that, in the O-poor conditions relevant to experiment, B forms the substitutional defect BCo and C forms the interstitial site Ci at the CoFe/MgO interface. The C-doped MTJ is predicted to have a significantly higher TMR than the B-doped MTJ. This is due to interface state densities associated with the majority spin Δ1-symmetry bands being more heavily suppressed ...


Persistent Spin Texture Enforced By Symmetry, L. L. Tao, Evgeny Y. Tsymbal Jul 2018

Persistent Spin Texture Enforced By Symmetry, L. L. Tao, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Persistent spin texture (PST) is the property of some materials to maintain a uniform spin configuration in the momentum space. This property has been predicted to support an extraordinarily long spin lifetime of carriers promising for spintronics applications. Here, we predict that there exists a class of noncentrosymmetric bulk materials, where the PST is enforced by the nonsymmorphic space group symmetry of the crystal. Around certain high symmetry points in the Brillouin zone, the sublattice degrees of freedom impose a constraint on the effective spin–orbit field, which orientation remains independent of the momentum and thus maintains the PST. We ...


Ambipolar Ferromagnetism By Electrostatic Doping Of A Manganite, L. M. Zheng, X. Renshaw Wang, W. M. Lü, C. J. Li, Tula R. Paudel, Z. Q. Liu, Z. Huang, S. W. Zeng, Kun Han, Z. H. Chen, X. P. Qiu, M. S. Li, Shize Yang, B. Yang, Matthew F. Chisholm, L. W. Martin, S. J. Pennycook, Evgeny Y. Tsymbal, J. M. D. Coey, W. W. Cao May 2018

Ambipolar Ferromagnetism By Electrostatic Doping Of A Manganite, L. M. Zheng, X. Renshaw Wang, W. M. Lü, C. J. Li, Tula R. Paudel, Z. Q. Liu, Z. Huang, S. W. Zeng, Kun Han, Z. H. Chen, X. P. Qiu, M. S. Li, Shize Yang, B. Yang, Matthew F. Chisholm, L. W. Martin, S. J. Pennycook, Evgeny Y. Tsymbal, J. M. D. Coey, W. W. Cao

Evgeny Tsymbal Publications

Complex-oxide materials exhibit physical properties that involve the interplay of charge and spin degrees of freedom. However, an ambipolar oxide that is able to exhibit both electron-doped and hole-doped ferromagnetism in the same material has proved elusive. Here we report ambipolar ferromagnetism in LaMnO3, with electron–hole asymmetry of the ferromagnetic order. Starting from an undoped atomically thin LaMnO3 film, we electrostatically dope the material with electrons or holes according to the polarity of a voltage applied across an ionic liquid gate. Magnetotransport characterization reveals that an increase of either electron-doping or hole-doping induced ferromagnetic order in this ...


Resonant Tunneling Across A Ferroelectric Domain Wall, M. Li, L. L. Tao, J. P. Velev, Evgeny Y. Tsymbal Apr 2018

Resonant Tunneling Across A Ferroelectric Domain Wall, M. Li, L. L. Tao, J. P. Velev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Motivated by recent experimental observations, we explore electron transport properties of a ferroelectric tunnel junction (FTJ) with an embedded head-to-head ferroelectric domain wall, using first-principles density-functional theory calculations. We consider a FTJ with La0.5Sr0.5MnO3 electrodes separated by a BaTiO3 barrier layer and show that an in-plane charged domain wall in the ferroelectric BaTiO3 can be induced by polar interfaces. The resulting V-shaped electrostatic potential profile across the BaTiO3 layer creates a quantum well and leads to the formation of a two-dimensional electron gas, which stabilizes the domain wall. The confined ...


Polarization-Controlled Modulation Doping Of A Ferroelectric From First Principles, Xiaohui Liu, Evgeny Y. Tsymbal, Karin M. Rabe Mar 2018

Polarization-Controlled Modulation Doping Of A Ferroelectric From First Principles, Xiaohui Liu, Evgeny Y. Tsymbal, Karin M. Rabe

Evgeny Tsymbal Publications

In a ferroelectric field effect transistor (FeFET), it is generally assumed that the ferroelectric gate plays a purely electrostatic role. Recently it has been shown that in some cases, which could be called “active FeFETs,” electronic states in the ferroelectric contribute to the device conductance as the result of a modulation doping effect in which carriers are transferred from the channel into the ferroelectric layers near the interface. Here we report first-principles calculations and model analysis to elucidate the various aspects of this mechanism and to provide guidance in materials choices and interface termination for optimizing the on-off ratio, using ...


Prediction Of A Mobile Two-Dimensional Electron Gas At The Lasco3/Basno3(001) Interface, Tula R. Paudel, Evgeny Y. Tsymbal Dec 2017

Prediction Of A Mobile Two-Dimensional Electron Gas At The Lasco3/Basno3(001) Interface, Tula R. Paudel, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Two-dimensional electron gases (2DEG) at oxide interfaces, such as LaAlO3/SrTiO3 (001), have aroused significant interest due to their high carrier density (∼1014 cm−2) and strong lateral confinement (∼1 nm). However, these 2DEGs are normally hosted by the weakly dispersive and degenerate d bands (e.g., Ti-3d bands), which are strongly coupled to the lattice, causing mobility of such 2DEGs to be relatively low at room temperature (∼1 cm2/Vs). Here, we propose using oxide host materials with the conduction bands formed from s electrons to increase carrier mobility and soften its temperature dependence. Using ...


Epitaxial Thin Films Of Dirac Semimetal Antiperovskite Cu3Pdn, C. X. Quintela, N. Campbell, D. F. Shao, J. Irwin, D. T. Harris, L. Lie, T. J. Anderson, N. Reiser, X. Q. Pan, Evgeny Y. Tsymbal, M. S. Rzchowski, C B. Eom Nov 2017

Epitaxial Thin Films Of Dirac Semimetal Antiperovskite Cu3Pdn, C. X. Quintela, N. Campbell, D. F. Shao, J. Irwin, D. T. Harris, L. Lie, T. J. Anderson, N. Reiser, X. Q. Pan, Evgeny Y. Tsymbal, M. S. Rzchowski, C B. Eom

Evgeny Tsymbal Publications

The growth and study of materials showing novel topological states of matter is one of the frontiers in condensed matter physics. Among this class of materials, the nitride antiperovskite Cu3PdN has been proposed as a new three-dimensional Dirac semimetal. However, the experimental realization of Cu3PdN and the consequent study of its electronic properties have been hindered due to the difficulty of synthesizing this material. In this study, we report fabrication and both structural and transport characterization of epitaxial Cu3PdN thin films grown on (001)-oriented SrTiO3 substrates by reactive magnetron sputtering and post-annealed ...


Model Of Orbital Populations For Voltage-Controlled Magnetic Anisotropy In Transition-Metal Thin Films, Jia Zhang, Pavel V. Lukashev, Sitaram Jaswal, Evgeny Y. Tsymbal Jul 2017

Model Of Orbital Populations For Voltage-Controlled Magnetic Anisotropy In Transition-Metal Thin Films, Jia Zhang, Pavel V. Lukashev, Sitaram Jaswal, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Voltage-controlled magnetic anisotropy (VCMA) is an efficient way to manipulate the magnetization states in nanomagnets and is promising for low-power spintronic applications. The underlying physical mechanism for VCMA is known to involve a change in the d orbital occupation on the transition-metal interface atoms with an applied electric field. However, a simple qualitative picture of how this occupation controls the magnetocrystalline anisotropy (MCA) and even why in certain cases the MCA has the opposite sign remains elusive. In this paper, we exploit a simple model of orbital populations to elucidate a number of features typical for the interface MCA, and ...


Spin-Polarized Two-Dimensional Electron Gas At Gdtio3/Srtio3 Interfaces: Insight From First-Principles Calculations, J. Betancourt, Tula R. Paudel, Evgeny Y. Tsymbal, J. P. Velev Jul 2017

Spin-Polarized Two-Dimensional Electron Gas At Gdtio3/Srtio3 Interfaces: Insight From First-Principles Calculations, J. Betancourt, Tula R. Paudel, Evgeny Y. Tsymbal, J. P. Velev

Evgeny Tsymbal Publications

Two-dimensional electron gases (2DEGs) at oxide interfaces have been a topic of intensive research due to their high carrier mobility and strong confinement. Additionally, strong correlations in the oxide materials can give rise to new and interesting physics, such as magnetism and metal-insulator transitions at the interface. Using first-principles calculations based on density functional theory, we demonstrate the presence of a highly spin-polarized 2DEG at the interface between the Mott insulator GdTiO3 and a band insulator SrTiO3. The strong correlations in the dopant cause ferromagnetic alignment of the interface Ti atoms and result in a fully spin-polarized 2DEG ...


Reversible Spin Texture In Ferroelectric Hfo2, L. L. Tao, Tula R. Paudel, Alexey Kovalev, Evgeny Tsymbal Jun 2017

Reversible Spin Texture In Ferroelectric Hfo2, L. L. Tao, Tula R. Paudel, Alexey Kovalev, Evgeny Tsymbal

Evgeny Tsymbal Publications

Spin-orbit coupling effects occurring in noncentrosymmetric materials are known to be responsible for nontrivial spin configurations and a number of emergent physical phenomena. Ferroelectric materials may be especially interesting in this regard due to reversible spontaneous polarization making possible a nonvolatile electrical control of the spin degrees of freedom. Here, we explore a technologically relevant oxide material, HfO2, which has been shown to exhibit robust ferroelectricity in a noncentrosymmetric orthorhombic phase. Using theoretical modelling based on density-functional theory, we investigate the spin-dependent electronic structure of the ferroelectric HfO2 and demonstrate the appearance of chiral spin textures driven by ...


Electronic Structure And Direct Observation Of Ferrimagnetism In Multiferroic Hexagonal Ybfeo3, Shi Cao, Kishan Sinha, Xin Zhang, Xiaozhe Zhang, Xiao Wang, Yuewei Yin, Alpha T. N’Diaye, Jian Wang, David J. Keavney, Tula R. Paudel, Yaohua Liu, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu Jun 2017

Electronic Structure And Direct Observation Of Ferrimagnetism In Multiferroic Hexagonal Ybfeo3, Shi Cao, Kishan Sinha, Xin Zhang, Xiaozhe Zhang, Xiao Wang, Yuewei Yin, Alpha T. N’Diaye, Jian Wang, David J. Keavney, Tula R. Paudel, Yaohua Liu, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu

Evgeny Tsymbal Publications

The magnetic interactions between rare-earth and Fe ions in hexagonal rare-earth ferrites (h-RFeO3), may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate the interaction strength between the rare-earth and Fe ions as well as the magnetic moment of the rare-earth ions, element-specific magnetic characterization is needed. Using x-ray magnetic circular dichroism, we have studied the ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in h-YbFeO3 at low temperature, with an ...


Giant Enhancement Of Magnetic Anisotropy In Ultrathin Manganite Films Via Nanoscale 1d Periodic Depth Modulation, Anil Rajapitamahuni, L. Zhang, Mark A. Koten, V. R. Singh, John D. Burton, Evgeny Y. Tsymbal, Jeffrey E. Shield, Xia Hong May 2016

Giant Enhancement Of Magnetic Anisotropy In Ultrathin Manganite Films Via Nanoscale 1d Periodic Depth Modulation, Anil Rajapitamahuni, L. Zhang, Mark A. Koten, V. R. Singh, John D. Burton, Evgeny Y. Tsymbal, Jeffrey E. Shield, Xia Hong

Evgeny Tsymbal Publications

The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La,Sr)MnO3 has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La0.67Sr0.33MnO3 (LSMO) films grown on (001) SrTiO3 substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along (110) directions, with a 50-fold enhanced anisotropy energy ...


On The Structural Origin Of The Single-Ion Magnetic Anisotropy In Lufeo3, Shi Cao, Xiaozhe Zhang, Tula R. Paudel, Kishan Sinha, Xiao Wang, Xuanyuan Jiang, Wenbin Wang, Stuart Brutsche, Jian Wang, Philip J. Ryan, Jong-Woo Kim, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu Apr 2016

On The Structural Origin Of The Single-Ion Magnetic Anisotropy In Lufeo3, Shi Cao, Xiaozhe Zhang, Tula R. Paudel, Kishan Sinha, Xiao Wang, Xuanyuan Jiang, Wenbin Wang, Stuart Brutsche, Jian Wang, Philip J. Ryan, Jong-Woo Kim, Xuemei Cheng, Evgeny Y. Tsymbal, Peter A. Dowben, Xiaoshan Xu

Evgeny Tsymbal Publications

Electronic structures for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectra shape and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states has not changed, the spectra are sensitive to the changes in the local environments of the Fe3+ and Lu ...


Engineering Interfacial Energy Profile By Changing The Substrate Terminating Plane In Perovskite Heterointerfaces, S. Roy, Alim Solmaz, John D. Burton, Mark Huijben, Guus Rijnders, Evgeny Y. Tsymbal, T. Banerjee Mar 2016

Engineering Interfacial Energy Profile By Changing The Substrate Terminating Plane In Perovskite Heterointerfaces, S. Roy, Alim Solmaz, John D. Burton, Mark Huijben, Guus Rijnders, Evgeny Y. Tsymbal, T. Banerjee

Evgeny Tsymbal Publications

Atomically engineered oxide heterointerfaces show a range of novel phenomena not present in their bulk form, thus providing an additional knob to tune the functional properties across such interfaces. Here we show that for an oxide Schottky interface between metallic SrRuO3 and semiconducting Nb doped SrTiO3 (Nb:STO) the terminating surface of the substrate plays a crucial role in determining the electronic transport across it. Interestingly this is achieved by engineering a monolayer of a charge-neutral SrO layer across the Schottky interface and not by the insertion of charged layers at the interface, as has been demonstrated earlier ...


Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He Jan 2016

Modification Of The G-Phonon Mode Of Graphene By Nitrogen Doping, Pavel V. Lukashev, Liuyan Zhao, Tula R. Paudel, Theanne Schiros, Noah Hurley, Evgeny Y. Tsymbal, Aron Pinczuk, Abhay Pasupathy, Rui He

Evgeny Tsymbal Publications

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We ...


Tunneling Anisotropic Magnetoresistance In A Magnetic Tunnel Junction With Half-Metallic Electrodes, John D. Burton, Evgeny Y. Tsymbal Jan 2016

Tunneling Anisotropic Magnetoresistance In A Magnetic Tunnel Junction With Half-Metallic Electrodes, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Tunneling anisotropic magnetoresistance (TAMR) is the difference in resistance of a magnetic tunnel junction due to a change in magnetization direction of one or both magnetic electrodes with respect to the flow of current. We present the results of first-principles density functional calculations of the TAMR effect in magnetic tunnel junctions with La0.7Sr0.3MnO3 (LSMO) electrodes and a SrTiO3 (STO) tunneling barrier. We find an ∼500% difference in resistance between magnetization in the plane and out of the plane. This large TAMR effect originates from the half-metallic nature of LSMO: When magnetization is ...


Electronic Structure And Stability Of The Ch3Nh3Pbbr3 (001) Surface, Xin Huang, Tula R. Paudel, Peter A. Dowben, Shuai Dong, Evgeny Y. Tsymbal Jan 2016

Electronic Structure And Stability Of The Ch3Nh3Pbbr3 (001) Surface, Xin Huang, Tula R. Paudel, Peter A. Dowben, Shuai Dong, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The energetics and the electronic structure of methylammonium lead bromine (CH3NH3PbBr3) perovskite (001) surfaces are studied based on density functional theory. By examining the surface grand potential, we predict that the CH3NH3Br-terminated (001) surface is energetically more favorable than the PbBr2-terminated (001) surface, under thermodynamic equilibrium conditions of bulk CH3NH3PbBr3. The electronic structure of each of these two different surface terminations retains some of the characteristics of the bulk, while new surface states are found near band edges which may affect the photovoltaic performance ...


Band Structure And Spin Texture Of Bi2Se3 3D Ferromagnetic Metal Interface, Jia Zhang, Julian P. Velev, Xiaoqian Dang, Evgeny Y. Tsymbal Jan 2016

Band Structure And Spin Texture Of Bi2Se3 3D Ferromagnetic Metal Interface, Jia Zhang, Julian P. Velev, Xiaoqian Dang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The spin-helical surface states in a three-dimensional topological insulator (TI), such as Bi2Se3, are predicted to have superior efficiency in converting charge current into spin polarization. This property is said to be responsible for the giant spin-orbit torques observed in ferromagnetic metal/TI structures. In this work, using first-principles and model tight-binding calculations, we investigate the interface between the topological insulator Bi2Se3 and 3d-transition ferromagnetic metals Ni and Co. We find that the difference in the work functions of the topological insulator and the ferromagnetic metals shift the topological surface states down about 0 ...